The Recovery of the World’s Most Endangered Sea Turtle Has Stalled
Decades of efforts to restore the Gulf of Mexico’s populations of critically endangered Kemp’s ridley sea turtles have stalled, and the species may be on the decline again, worrying new research reveals.
Kemp’s ridley sea turtles, the world’s rarest sea turtle species, nearly went extinct in the second half of the last century after fishing nets devastated their populations. By 1985 the species was down to its last 200 to 250 breeding females.
Habitat protection and conservation efforts helped turn that around, including the introduction of devices that allow sea turtles to escape fishing nets. Populations began rebounding during the 1990s, rising as much as 15 percent a year.
“I considered it a gold star for how you do conservation,” said Thane Wibbels, a professor of biology at the University of Alabama at Birmingham and one of the authors of the new study. “It restored a species that was almost literally extinct.”
That recovery has now stopped. Kemp’s ridley sea turtles laid eggs in just 14,000 nests last year, a 34 percent decline from 2009. Even worse, the new research—published in the journal Ecosphere—finds that nesting levels are now just a fraction of what they were back in 1947, when Kemp’s ridley turtles laid an estimated 120,000 to 180,000 nests.
Those 1947 numbers—the first detailed calculation of historic nesting rates—reveal that the species is actually in much worse shape than was previously thought.
Researchers made the calculation by looking at a famous 1947 film that captured images of a mass-nesting event, called an arribada, at the species’ primary nesting site in Rancho Nuevo, Mexico. Then they compared the film with nesting density rates in current arribadas, something that couldn’t be done until recovery efforts allowed mass nesting to start again, to come up with an estimate of historic activity.
So why has recovery stalled? One possible explanation is the 2010 Deepwater Horizon oil disaster. “The Deepwater Horizon spill occurred in a very critical area for Kemp’s ridley,” Wibbels said. “It didn’t occur in nesting beaches, but it did occur in very well known and possibly important foraging grounds and developmental habitats.”
The spill area is also an important migratory corridor: Most female turtles pass through it on their way to and from the nesting beach at Rancho Nuevo. Hatchlings, which already have a low survival rate owing to predation, also travel on currents through the same region.
Another possibility is that the Gulf of Mexico may no longer be able to support a large number of sea turtles. Wibbels pointed out that blue crabs, one of the turtles’ favorite foods, are in decline in many areas of the Gulf.
Other prey species may also be suffering, he said. “There may not be the resources out there for these animals.”
The future of the Kemp’s ridley remains uncertain. “It’s possible that they’re going to keep going down, or they could maintain themselves at this level,” Wibbels said. He believes ongoing monitoring will be necessary to understand how well the turtles are reproducing, how many are surviving, and how well the ecosystem can support them in the future, if it can continue to do so at all.